The invention concerns a method and apparatus for operating a safety device for motor vehicles.
A known safety circuit of this type in the form of an isolating switching device for motor vehicles is presented in DE 33 27 532 A1. It responds primarily to electrical instructions from an emergency instruction transmitter, that is to say it can be switched under remote control and permits the battery to be isolated from the vehicle""s electrical system; however, it permits this not only in emergency cases but also when the vehicle is parked. Such a stationary vehicle turn-off circuit is, owing to an prevention circuit, permitted only when the engine is stationary or if no other current loads are connected into the circuit in the motor vehicle. However, it is a problem here that, in order to maintain its operational readiness, the control circuit remains connected to the battery even when disconnection from the vehicle""s electrical system has taken place, and said control circuit continues to consume current, that is to say cannot be used for a relatively long stationary period of the vehicle or relatively long period of overseas transportation. The disconnection of the battery from the vehicle""s electrical system is ultimately carried out by means of self-latching relays which possibly experience contact problems or tend towards contact sticking at the very high currents which occur here.
In modern motor vehicles, the number of electrical control units is increasing at an ever faster rate in accordance with the number of loads dependent on a vehicle""s electrical system, with the result that, in order to increase the operational reliability, the control units are usually networked by means of a vehicle-internal bus system and receive digital switching signals from a central control device in a type of ring circuit, said switching signals being decrypted in the control units using microprocessors and being converted into appropriate instructions to the directly adjacent receivers.
Such databus systems in a motor vehicle are usually based on the so-called CAN standard (Controller Area Network). Therefore, as a rule, the control units and the microprocessors arranged in them change into a quiescent or sleeping mode after a delay time, dependent on the type of control unit, after the vehicle has been deactivated. In this state, the quiescent current consumption of the control unit is relatively low, but in total it can still amount to a current of several hundred mA which permanently loads a vehicle battery, in particular if a primed monitoring system is added to this.
If such a vehicle is then stationary over a relatively long time without the battery being able to be loaded by the generator when the engine is running, for example during a relatively long period of absence of the keeper of the vehicle, when the vehicle is taken out of service for the winter or during a relatively long period of transportation overseas by ship, such severe discharge may occur, in conjunction with the self-discharge of the battery which always occurs and which cannot be avoided, that under certain circumstances even the vehicle battery is irreparably damaged, or at any rate it is no longer possible for the vehicle to be started.
Such exhaustive discharge of batteries also gives rise to lasting damage because during normal operation the electrical voltage which is generated by the electrical charge at the electrodes protects said electrodes against the aggressiveness of the sulphuric acid. If this voltage collapses owing to an exhaustive discharge, the protection of the electrodes also fails and disintegration phenomena occur, which even after a short time damage the electrodes irreparably to such an extent that the drastic damage to the storage capacity destroys the storage function of the battery.
A vehicle with a highly discharged battery is frequently reactivated, that is to say started up, by starting using external means by connecting a second battery, usually originating from another vehicle, in parallel with the discharged vehicle battery. However, in such a case it is not unusual, especially at night, for the poles to be mixed up, as a result of which not only the vehicle battery which is in any case greatly weakened but also the electrical devices and control units in the vehicle, that is to say the entire electrical system of the vehicle including the generator and generator diodes as well as the electronics can suffer lasting damage.
If the vehicle""s own, in this respect first, battery is very exhaustively discharged, an attempt at starting by external means can also fail because the voltage of the vehicle""s electrical system can drop, as a result of the high current which the starter and furthermore also the exhaustively discharged first battery require during the starting time, below a limiting value of, for example, 5 volts, and the control units which are important for starting can thus no longer be supplied with sufficient voltage.
In addition, when vehicle accidents occur, it is occasionally found that electrical leads, but also equipment, are damaged especially in the case of an accident which is primarily in the engine compartment (area at risk during a crash), which can lead to a spark flashover or an arc if there is a short circuit. As a result, if fuel escapes at the same time, for example due to damaged lines, fires may occur.
Therefore, in motor vehicle electrical systems, problems are posed by the (automatic) protection of the installed vehicle battery against exhaustive discharge, such as may occur, for example, during transportation overseas, when the vehicle is stationary for a relatively long time, and when there is excessive loading and thus corresponding discharging, by the protection of the vehicle""s electrical system and its components against polarity reversal, by the disconnection of at least electrical vehicle components which are at risk during a crash and of leads during a possible accident, and finally by the need to restore the basic setting in the event of disconnection occurring between the vehicle""s electrical system and the battery, i.e. to return the vehicle to a normal state.
It is currently known to ensure protection of the battery against exhaustive discharge during transportation overseas by disconnecting the battery manually from the vehicle""s electrical system using an isolating switch after the vehicle has been loaded onto the ship. During unloading, that is to say so that the vehicle can be driven off the ship, the isolating switch is closed again and ultimately removed by the appropriate dealer before the vehicle is ultimately put into service.
The aforementioned problem of incorrect polarity in the case of an external starter device is particularly serious because the damage can be overcome only by replacing, at a correspondingly high cost, the inadequately protected electrical and electronic components which have been irreparably damaged by the incorrect polarity.
The following specifications relate to known battery isolating switches and to the possibility of disconnecting a battery from its loads under certain circumstances if there is a risk of exhaustive discharge:
DE 34 02 372 A1, DE 42 11 578 C1, DE 33 03 185 A1, DE-B 1 086 322.
Thus, in DE 34 02 732 A1, two conductive electrodes which lie coaxially one opposite the other are disconnected by means of an insulator element which is located between them but which in normal circumstances is bridged by an electrically conductive switching bridge. The switching bridge can be opened by axially displacing a sheath.
DE 42 11 578 C1 presents a battery isolating device for motor vehicles having a battery isolating switch which can be actuated manually from the battery space and under remote control from the driver""s seat with a main safety switch. Before the battery isolating switch is possibly opened, all the loads which are connected to the ignition lock must firstly be switched off and an engine turning-off procedure must be initiated.
A further battery isolating switch which is known from DE 33 03 185 A1 has, firstly, a handle for manually switching it on and off as desired, by means of cam running tracks arranged in a sheath, and, secondly, actuation in order to turn it off can also be triggered by another power source, for example an explosive cartridge which can be triggered by a pulse as a function of the triggering of a fire detector.
Furthermore, polarity reversal prevention devices are known, for example in battery chargers or when batteries are connected to the electrical systems of motor vehicles, from DE 42 31 970 C2 or DE 196 03 117 A1.
The known arrangements for the prevention of polarity reversal for a battery charging system and/or an electrical system for motor vehicles are usually are based on the fact that a sensor circuit is provided which senses the polarity of the battery which is to be connected and permits connection, for example by closing a switch, to a charger or to a vehicle""s electrical system only if the polarity is correct.
The circuit for protecting against polarity reversal for a battery charger corresponding to DE 42 31 970 C2 operates in such a way that a microprocessor which senses the polarity reversal supplies the connection point for the positive pole of the battery which is to be charged with a positive voltage, via a voltage divider, even if the microprocessor cannot reliably detect correct polarity at a first detection input. In fact, when there is incorrect polarity across this voltage device, a measuring voltage for evaluation by the microprocessor is detected at the voltage divider which is so severely shifted in the direction of negative values that, in the event of polarity reversal, a correct polarity reversal message can be output and appropriate measures taken, for example the polarity of the terminals can be reversed.
In the polarity reversal prevention circuit according to DE 196 03 117 A1, MOSFET transistors are provided by means of which the voltage drop caused by the protection circuit is significantly reduced so that the protection circuit can be used even with low dc voltages.
In addition, DE-B 1 086 322 discloses an electrical high-voltage switch in which an axially moveable pin-shaped switching contact and two fixed contacts which cooperate with it are provided. Both the switching contact and the fixed contacts are arranged in a switchroom which is surrounded by a double-walled casing. This ensures that at any rate, owing to the metallic nature of the outer wall of the switchroom, parts with a large field strength lie outside the switchroom. There are no connections to a battery isolating switch operating with low voltage.
It is known, in addition, that in a discharge protection circuit for the current accumulator in a motor vehicle (DE 40 40 405 A1) a self-latching circuit is provided which becomes active when the vehicle is switched off and then reliably electrically disconnects loads which are still switched on from the current accumulator by actuating an electrical isolating switch device.
In addition, in a device for protecting a main current path in a transportation means, it is known (DE 41 10 240 C1) to arrange an electronically drivable turn-off means which is accommodated near to the battery and has the purpose of bringing about a controlled disconnection between the main current path and the battery as soon as a current which is characteristic of a short-circuit situation is detected. The turn-off means can be, for example, an electromagnetic actuator or else an explosive capsule.
The invention is based on the object of ensuring, on the one hand, that a disconnection procedure, that is to say isolation of the battery from the vehicle""s electrical system, which is to be carried out for a multiplicity of reasons is possible quickly and without difficulty, in which case, in order to avoid exhaustive discharge of the battery, the element which performs the switching over is itself isolated from the vehicle""s electrical system, but on the other hand of ensuring that the vehicle can be re-activated, that is to say the battery can be connected to the vehicle""s electrical system, at any time without a relatively large amount of effort and installation work.
A method according to this invention uses a standardized device that both disconnects, preferably automatically, the battery from the vehicle""s electrical system for transportation, in the event of the vehicle being stationary for a relatively long period or even an accident, and also ensures that, when the vehicle has absolutely zero current, the power supply to the safety device which is also cut off from the power supply by its own preceding isolation measure is restored by an operator opening one of the doors of the vehicle.
As a result, power connection lines to the safety device are closed by means of appropriate door contacts, and said lines can then connect the entire vehicle""s electrical system to the battery again by means of the motor drive, actuated by said safety device, for the battery isolating switch.
This connection is made, at any rate, whenever there are no other inhibiting signals present.
It is therefore possible to assign a plurality of essential functions to the safety device, composed of multistage, motor-driven battery isolating switch, switching logic and associated sensor system, i.e. to make optimum use of the safety facilities which are provided by such a multistage isolating switch, and at the same time make available a high degree of operating convenience to the user of the vehicle.
In addition, the arrangement of a connector for starter aids in the vicinity of the high-current isolating switch, which, as an starting circuit-breaker, is part of the safety device, is advantageous. The connector for starter aids can be connected, for example, to the positive pole of an auxiliary battery, for example by means of a jump lead, or else to some other device which has the purpose of promoting the starting of a vehicle and which supplies an appropriately high starter current, for example to a drivable rectifier circuit which is fed with an alternating power-system voltage or can itself be used as a starter aid for a third vehicle.
It is also advantageous that the respectively occurring switching procedures do not make use of any relays which are unsuitable for the currents occurring here under extreme circumstances, for example possibly several hundred amps in the case of a starting process which runs from the connector for external starter means. In order to connect the various terminals, specifically the vehicle""s electrical system, battery, connector for starting aids, loads which are at risk in an accident, a displaceable contact bridge is provided on a contact carrier. The contact bridge is driven by electrical positioning means, for example by motor-operated actuation, but hydraulic or electromagnetic drive means may also be provided.